The US has spent $40 billion on the ground-based midcourse ballistic-missile-defense system.

By the end of 2017, the US wants to have 44 missile interceptors stationed in Alaska and California to fend off a possible nuclear-missile attack.

While the ground-based midcourse missile-defense system has had some success in tests, real-world conditions could easily stress the system to the max, leaving the US vulnerable to nuclear attacks.

On the other hand, Russia has 68 nuclear-tipped ballistic-missile interceptors around Moscow. US missiles interceptors do not have explosive payloads and have to actually slam into an incoming warhead to incapacitate it.

“We have to actually hit a bullet with a bullet,” Bruce Blair, a former US nuclear-launch officer and an expert on nuclear security, told Business Insider. “The general expert estimate is that any one interceptor in the US side would have no better than a 25% chance of making impact with a Russian nuclear warhead.” So the US would have to fire at least four interceptors to every one missile threat.

So with the US’s 44 interceptors, “at most you could destroy 11 warheads,” Blair said, “and Russia could throw 1,000 at us.”

Read the whole story from Business Insider.

Featured image courtesy of the Missile Defense Agency